Detection system and detection method

ABSTRACT

According to an embodiment, a detection system includes a plurality of first sensors, a second sensor, a first calculator, and a second calculator. Each of the first sensors is configured to detect an elastic wave generated from a structure, and convert the elastic wave into a detection signal. The second sensor is configured to detect a noise propagating from surroundings, and convert the noise into a reference signal. The first calculator is configured to calculate a plurality of difference detection signals based on the respective detection signals and the reference signal. The second calculator is configured to calculate a position of a generation source of the elastic wave from the plurality of difference detection signals.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. application Ser. No.15/070,981, filed Mar. 15, 2016, which is based upon and claims thebenefit of priority from Japanese Patent Application No. 2015-059491,filed on Mar. 23, 2015; the entire contents of which are incorporatedherein by reference.

FIELD

Embodiments described herein relate generally to a detection system anda detection method.

BACKGROUND

In recent years, problems associated with aging of structures such asbridges built during the period of rapid economic growth becomeactualized. Damages of if accidents occur in the structures areincalculable. Therefore, technologies for monitoring states of thestructures are known. For example, technologies for detecting damage ofthe structures by an acoustic emission (AE) system that detects elasticwaves generated in association with generation of internal cracks ordevelopment of the internal cracks by high-sensitive sensors are known.

The acoustic emission is an elastic wave generated in association withdevelopment of fatigue cracks of material. In the AE system, thiselastic wave is detected by an AE sensor using a piezoelectric elementas a voltage signal (AE signal). The AE signal is detected as apremonition before rupture of the material is caused, and thus thefrequency of generation of the AE signal and signal intensity of the AEsignal are useful as indexes that indicate soundness of the material.Therefore, technologies for detecting an indication of deterioration ofstructures by the AE system have been actively studied. Especially, incorrosion diagnosis of oil tanks, manufacturing processes of mechanicaldevices, and the like, the detection technologies of the AE system havebeen widely used mainly in Europe and the United States, andstandardization of the detection technologies of the AE system has beenperformed.

The AE signal is typically a feeble signal and a signal level thereofneeds to be increased using an amplifier having high degree ofamplification, and thus the AE signal is susceptible to noises whilebeing highly sensitive. Therefore, in conventional technologies, thenoises that are significant enough to cause erroneous determination ofAE signal detection may be superimposed depending on an AE signaldetection environment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a configuration of adetection system of an embodiment;

FIG. 2 is a diagram for describing a first example of a typical approachpath of noises;

FIG. 3 is a diagram for describing a second example of the typicalapproach path of noises;

FIG. 4 is a diagram illustrating a first example of a positionalrelationship between a first sensor and a second sensor of anembodiment;

FIG. 5 is a diagram illustrating a second example of a positionalrelationship between the first sensor and the second sensor of anembodiment;

FIG. 6 is a diagram illustrating a first example of a positionalrelationship between the first sensor and the second sensor of anembodiment;

FIG. 7 is a diagram illustrating a second example of a positionalrelationship between the first sensor and the second sensor of anembodiment;

FIG. 8 is a conceptual diagram of noise canceling by a signal processingdevice of an embodiment;

FIG. 9A is a diagram illustrating an example of a detection signal (withnoises) of an embodiment;

FIG. 9B is a diagram illustrating an example of a difference detectionsignal (without noises) of an embodiment;

FIG. 10 is a diagram illustrating an example of propagating speedinformation of an embodiment;

FIG. 11 is a diagram for describing an example of a position calculationmethod of an embodiment (in a case of one dimension);

FIG. 12 is a diagram for describing an example of a position calculationmethod of an embodiment (in a case of two dimensions);

FIG. 13 is a diagram for describing an example of a position calculationmethod of an embodiment (in a case of two dimensions);

FIG. 14 is a diagram illustrating an example of a functionalconfiguration of a server device of an embodiment;

FIG. 15 is a diagram illustrating an example of display informationindicating positional information of an embodiment;

FIG. 16 is a diagram illustrating an example of display informationindicating cumulative energy of an embodiment;

FIG. 17 is a flowchart illustrating an example of a detection method(signal selection processing) of an embodiment;

FIG. 18 is a flowchart illustrating an example of a detection method(position information calculation processing) of an embodiment;

FIG. 19 is a flowchart illustrating an example of a detection method(display processing) of an embodiment; and

FIG. 20 is a diagram illustrating an example of a hardware configurationof a server device of an embodiment.

DETAILED DESCRIPTION

According to an embodiment, a detection system includes a plurality offirst sensors, a second sensor, a first calculator, and a secondcalculator. Each of the first sensors is configured to detect an elasticwave generated from a structure, and convert the elastic wave into adetection signal. The second sensor is configured to detect a noisepropagating from surroundings, and convert the noise into a referencesignal. The first calculator is configured to calculate a plurality ofdifference detection signals based on the respective detection signalsand the reference signal. The second calculator is configured tocalculate a position of a generation source of the elastic wave from theplurality of difference detection signals.

Hereinafter, embodiments of a detection system and a detection methodwill be described in detail with reference to the appended drawings.

FIG. 1 is a diagram illustrating an example of a configuration of adetection system 1 of an embodiment. The detection system 1 of anembodiment includes first sensors 10 a to 10 d, a second sensor 11, anda signal processing device 20.

The first sensors 10 a to 10 d and the second sensor 11 are installed ina structure such as a bridge. The first sensors 10 a to 10 d detect anelastic wave (an AE wave) generated from the structure, and convert theelastic wave into electrical signals such as voltage signals.Hereinafter, these electrical signals are referred to as detectionsignals. Further, when the first sensors 10 a to 10 d are notdistinguished, they are simply called first sensor 10.

Meanwhile, the second sensor 11 detects noises (electrical noises)propagating from surroundings of the second sensor 11, and converts thenoises into an electrical signal such as a voltage signal. Hereinafter,this electrical signal is referred to as reference signal. Here, thenoises will be described.

FIG. 2 is a diagram for describing a first example of a typical approachpath of noises. The example of FIG. 2 illustrates a case of a signalprocessing device 100 that receives a signal from a sensor 103 installedin a metal 102 through an amplifier 104 and an amplifier 105. A noisesource 101 is, for example, a separate device (circuit) from the signalprocessing device 100. The noises approach the sensor 103 from the noisesource 101 through the metal 102, and the noises approach the signalprocessing device 100 through the amplifiers 104 and 105. Further, thenoises approach the signal processing device 100 from a ground of theamplifier 104 and a ground of the amplifier 105 through the metal 102.

FIG. 3 is a diagram for describing a second example of a typicalapproach path of noises. The example of FIG. 3 illustrates a case of thesignal processing device 100 that receives a signal from the sensor 103through the amplifiers 104 and 105. A noise source 106 is anelectromagnetic wave emitted from a separate device from the signalprocessing device 100. The noises propagates in the air from the noisesource 106 to the sensor 103, and to a signal line between the sensor103 and the signal processing device 100, thereby to approach the signalprocessing device 100.

Referring pack to FIG. 1, piezoelectric elements having sensitivity in arange from 10 kHz to 1 MHz are used for the first sensor 10 and thesecond sensor 11. Examples of types of the first sensor 10 and thesecond sensor 11 include a resonance type having a resonance peak in afrequency range, a broadband type that suppresses resonance, or thelike. The first sensor 10 and the second sensor 11 may employ any type.Further, the first sensor 10 and the second sensor 11 may have apre-amplifier built-in. Further, examples of a detection method by thefirst sensor 10 and the second sensor 11 include a voltage output type,a resistance change type, and an electrostatic capacity type, and thelike. Any detection method may be employed.

The signal processing device 20 of an embodiment includes a firstamplifier 21, a second amplifier 22, a first calculator 23, a switchunit 24, a generator 25, an adjuster 26, an extractor 27, a secondcalculator 28, and a communication unit 29. The first amplifier 21includes an amplifier 21 a, an amplifier 21 b, an amplifier 21 c, and anamplifier 21 d. The first calculator 23 includes a differentialcalculator 23 a, a differential calculator 23 b, a differentialcalculator 23 c, and a differential calculator 23 d.

Operations of the amplifier 21 a, the amplifier 21 b, the amplifier 21c, and the amplifier 21 d, and operations of the differential calculator23 a, the differential calculator 23 b, the differential calculator 23c, and the differential calculator 23 d are similar. Therefore,description will be given using cases of the amplifier 21 a and thedifferential calculator 23 a as examples.

When having received a detection signal S_(10a) from the first sensor 10a, the amplifier 21 a amplifies the detection signal S_(10a). Theamplifier 21 a then inputs the amplified detection signal S_(10a) to thedifferential calculator 23 a and the switch unit 24. Further, whenhaving received a feedback signal that adjusts the degree ofamplification of the detection signal S_(10a) from the adjuster 26, theamplifier 21 a adjusts the degree of amplification of the detectionsignal S_(10a) based on the feedback signal. Hereinafter, forsimplification, the amplified detection signal S_(10a) is also simplyreferred to as detection signal S_(10a).

Meanwhile, when having received a reference signal S₁₁ from the secondsensor 11, the second amplifier 22 amplifies the reference signal S₁₁.The second amplifier 22 then inputs the amplified reference signal S₁₁to the differential calculator 23 a, the differential calculator 23 b,the differential calculator 23 c, and the differential calculator 23 d.Further, when having received the feedback signal that adjusts thedegree of amplification of the reference signal S₁₁ from the adjuster26, the second amplifier 22 adjusts the degree of amplification of thereference signal S₁₁ based on the feedback signal. Hereinafter, forsimplification, the amplified reference signal S₁₁ is also simplyreferred to as reference signal S₁₁.

When having received the detection signal S_(10a) from the amplifier 21a, and the reference signal S₁₁ from the second amplifier 22, thedifferential calculator 23 a calculates a difference detection signalS_(10a)-S₁₁ by subtracting the reference signal S₁₁ from the detectionsignal S_(10a). Accordingly, the differential calculator 23 a removes anoise component superimposed on the first sensor 10 a and the secondsensor 11 at the same phase. The differential calculator 23 a inputs thedifference detection signal S_(10a)-S₁₁ from which the noises have beencanceled to the switch unit 24.

Similarly, the differential calculator 23 b inputs a differencedetection signal S_(10b)-S₁₁ from which the noises have been canceled tothe switch unit 24. The differential calculator 23 c inputs a differencedetection signal S_(10c)-S₁₁ from which the noises have been canceled tothe switch unit 24. The differential calculator 23 d inputs a differencedetection signal S_(10d)-S₁₁ from which the noises have been canceled tothe switch unit 24.

Note that the second sensor 11 that outputs the reference signal S₁₁also detects the elastic waves. Here, a method of not detecting theelastic waves as the reference signal by the second sensor will bedescribed.

FIG. 4 is a diagram illustrating a first example of a positionalrelationship between the first sensor 10 and the second sensor 11. Theexample of FIG. 4 illustrates a case of installing the first sensor 10a, the first sensor 10 b, and the second sensor 11 when the structurecan be regarded as a one-dimensional object to be measured. A distancebetween the first sensor 10 a and the first sensor 10 b is a. In thiscase, the second sensor 11 is arranged in a position separated from theclosest first sensor 10 b by a distance b (b>a). Accordingly, theelastic wave generated from a measurement range first reaches firstsensor 10 a and the first sensor 10 b, and then reaches the secondsensor 11 with a sufficient time difference. Therefore, the positionalrelationship among the first sensor 10 a, the first sensor 10 b, and thesecond sensor 11 is set as illustrated in FIG. 4, so that the secondsensor 11 can temporally separate the noises and the elastic wave.

FIG. 5 is a diagram illustrating a second example of a positionalrelationship between the first sensor 10 and the second sensor 11. Theexample of FIG. 5 illustrates a case of not installing the second sensor11 from installation positions of the first sensor 10 a and the firstsensor 10 b with a sufficient distance. In this case, a silencingmaterial 12 is installed between the second sensor 11 and an object tobe measured, so that the elastic wave reaching the second sensor 11 isattenuated or reflected. The silencing material 12 is a material thatattenuates the elastic wave or a material having different acousticimpedance from the object to be measured. The acoustic impedance isdefined by a product of a sound speed in a medium and density, and is46.4×10⁶ [kg/m²s] in iron. In this case, as a material having acousticimpedance that is 10 times or more different from iron, for example,rubber (1.5×10⁶ [kg/m²s]), wood (2×10⁶ [kg/m²s]), acrylic (3.3×10⁶[kg/m²s]), epoxy resin (3×10⁶ [kg/m²s]), water (1.5×10⁶ [kg/m²s]), air(428 [kg/m²s]), or the like can be used. The silencing material 12 isinstalled as illustrated in FIG. 5, so that the elastic wave cannotreach the second sensor 11. Therefore, the second sensor 11 can separatethe noises and the elastic wave.

FIG. 6 is a diagram illustrating a first example of a positionalrelationship between the first sensor 10 and the second sensor 11. Theexample of FIG. 6 illustrates a case of installing the first sensor 10a, the first sensor 10 b, the first sensor 10 c, the first sensor 10 d,and the second sensor 11 when the structure can be regarded as atwo-dimensional object to be measured. When a maximum distance betweenthe first sensors 10 is a, the maximum distance a is a distance betweenthe first sensor 10 a and the first sensor 10 c (the first sensor 10 band the first sensor 10 d). In this case, the second sensor 11 isarranged in a position separated from the closest first sensor 10 a by adistance b (b>a). Accordingly, the elastic wave generated from themeasurement range first reaches the four first sensors 10 a to 10 d, andthen reaches the second sensor 11 with a sufficient time difference.Therefore, the positional relationship among the first sensor 10 a, thefirst sensor 10 b, the first sensor 10 c, the first sensor 10 d, and thesecond sensor 11 is set as illustrated in FIG. 6, whereby the secondsensor 11 can temporally separate the noises and the elastic wave.

FIG. 7 is a diagram illustrating a second example of a positionalrelationship between the first sensor 10 and the second sensor 11. Theexample of FIG. 7 illustrates a case of not being able to install thesecond sensor 11 with a sufficient distance from installation positionsof the first sensor 10 a, the first sensor 10 b, the first sensor 10 c,and the first sensor 10 d. Description of FIG. 7 is similar to the onedimensional case of FIG. 5, and is thus omitted.

Referring back to FIG. 1, the switch unit 24 includes a switch 24 a, aswitch 24 b, a switch 24 c, and a switch 24 d.

The switch unit 24 inputs either the detection signal S_(10a) or thedifference detection signal S_(10a)-S₁₁ to the generator 25, theadjuster 26, and the extractor 27 through an AD converter (ADC) (notillustrated in FIG. 1) by switching the switch 24 a.

When having received the detection signal S_(10a) from which the noisecomponent has been removed, the ADC quantizes and converts the detectionsignal S_(10a) from which the noise component has been removed into adigital detection signal S_(10a). The ADC inputs the digital detectionsignal S_(10a) to the generator 25, the adjuster 26, and the extractor27.

Similarly, the switch unit 24 inputs either the detection signal S_(10b)or the difference detection signal S_(10b)-S₁₁ to the generator 25, theadjuster 26, and the extractor 27 through an ADC (not illustrated inFIG. 1) by switching the switch 24 b. Further, the switch unit 24 inputseither the detection signal S_(10c) or the difference detection signalS_(10c)-S₁₁ to the generator 25, the adjuster 26, and the extractor 27through an ADC (not illustrated in FIG. 1) by switching the switch 24 c.Further, the switch unit 24 inputs either the detection signal S_(10d)or the difference detection signal S_(10d)-S₁₁ to the generator 25, theadjuster 26, and the extractor 27 through an ADC (not illustrated inFIG. 1) by switching the switch 24 d.

To be specific, the generator 25 inputs, to the switch unit 24 and theextractor 27, a gate signal (selection signal) that switches the switch24 a (the switch 24 b, the switch 24 c, or the switch 24 d) to an outputof the difference detection signal S_(10a)-S₁₁ (S_(10b)-S₁₁,S_(10c)-S₁₁, or S_(10d)-S₁₁) until a predetermined time T passes, whenany one of the detection signals S_(10a) to S_(10d) received from theswitch unit 24 is a threshold (second threshold) or more. Thepredetermined time T is a processing time of the extractor 27. To bespecific, the predetermined time T is a/v (a: a maximum distance betweenthe first sensors 10, and v: a propagating speed of the elastic wave).Details of the processing of the extractor 27 will be described below.

FIG. 8 is a conceptual diagram of noise canceling by the signalprocessing device 20 of an embodiment. The example of FIG. 8schematically illustrates outputs of the first sensors 10 a to 10 d, andthe second sensor 11. When the elastic wave is generated from thestructure, time differences according the positions of the first sensors10 a to 10 d and the second sensor 11 are caused at times when the firstsensors 10 a to 10 d and the second sensor 11 detect the elastic wave.In the case of the example of FIG. 6, the time difference between thetime when the first sensor 10 a has first detected the elastic wave andthe time when the second sensor 11 detects the elastic wave becomes atleast a/v (a: a maximum distance between the first sensors 10 and v: apropagating speed of the elastic wave) or more. Meanwhile, the noisesare superimposed on the first sensors 10 a to 10 d and the second sensor11 at the same time.

Therefore, the first calculator 23 can cancel the noises by subtractingthe reference signal S₁₁ from the second sensor 11, from the detectionsignals S_(10a), S_(10b), S_(10c), and S_(10d) from the first sensors 10a to 10 d. Further, when the elastic wave has first reached the firstsensor 10 a, the first calculator 23 performs calculation processingwithin the range of the predetermined time T=a/v determined according tothe installation positions of the first sensors 10 a to 10 d and thematerial of the structure, from the time when the first sensor 10 a hasdetected the elastic wave, thereby to prevent the elastic wave leakedand transmitted to the second sensor 11 from being erroneouslydetermined as a noise.

To be specific, the switch unit 24 switches the switch 24 a (the switch24 b, the switch 24 c, or the switch 24 d) to an output of thedifference detection signal S_(10a)-S₁₁ (S_(10b)-S₁₁, S_(10c)-S₁₁, orS_(10d)-S₁₁) by a gate signal that becomes Hi during the predeterminedtime T. Accordingly, the difference detection signals S_(10a)-S₁₁,S_(10b)-S₁₁, S_(10c)-S₁₁, and S_(10d)-S₁₁ are being input to thegenerator 25, the adjuster 26, and the extractor 27 until thepredetermined time T passes. Note that the generator 25 does not performthe above-described threshold determination of switching the switch unit24 while the gate signal is Hi.

Further, when the gate signal is changed from Hi to Lo due to the elapseof the predetermined time T, the switch unit 24 switches the switch 24 a(the switch 24 b, the switch 24 c, or the switch 24 d) to outputs of thedetection signal S_(10a) (S_(10b), S_(10c), or S_(10d)) again.Accordingly, the detection signals S_(10a), S_(10b), S_(10c), andS_(10d) are input to the generator 25 and the adjuster 26 again.

FIG. 9A is a diagram illustrating an example of the detection signal S₁₀(with noises) of an embodiment. Meanwhile, FIG. 9B is a diagramillustrating an example of the difference detection signal S₁₀-S₁₁(without noises). As illustrated in FIG. 9B, in the difference detectionsignal S₁₀-S₁₁, the noises included in the detection signal S₁₀ arecanceled.

Referring back to FIG. 1, further, when having received the detectionsignal S_(10a) (S_(10b), S_(10c), or S_(10d)), or the differencedetection signal S_(10a)-S₁₁ (S_(10b)-S₁₁, S_(10c)-S₁₁, or S_(10d)-S₁₁)from the switch unit 24, the adjuster 26 adjusts the degree ofamplification of the first amplifier 21 or the second amplifier 22 basedon the detection signal S_(10a) (S_(10b), S_(10c), or S_(10d)), or thedifference detection signal S_(10a)-S₁₁ (S_(10b)-S₁₁, S_(10c)-S₁₁, orS_(10d)-S₁₁). When adjusting the degree of amplification of thedetection signal S_(10a) (S_(10b), S_(10c), or S_(10d)), the adjuster 26inputs the feedback signal that adjusts the degree of amplification ofthe detection signal S_(10a) (S_(10b), S_(10c), or S_(10d)) to theamplifier 21 a (21 b, 21 c, or 21 d). When adjusting the degree ofamplification of the reference signal S₁₁, the adjuster 26 inputs thefeedback signal that adjusts the degree of amplification of thereference signal S₁₁ to the second amplifier 22.

When the gate signal input from the generator 25 is Hi, the extractor 27receives the difference detection signals S_(10a)-S₁₁ to S_(10d)-S₁₁from the switch unit 24. The extractor 27 stores the time informationthat indicates the times when the extractor 27 has received therespective difference detection signals S_(10a)-S₁₁ to S_(10d)-S₁₁. Theextractor 27 extracts the feature amount information from the respectivedifference detection signals S_(10a)-S₁₁ to S_(10d)-S₁₁. The respectivepieces of feature amount information of the difference detection signalsS_(10a)-S₁₁ to S_(10d)-S₁₁ are similar, and thus a case of thedifference detection signal S_(10a)-S₁₁ will be described as an example.

The feature amount information of the difference detection signalS_(10a)-S₁₁ exhibits the feature of the difference detection signalS_(10a)-S₁₁. The feature amount information of the difference detectionsignal S_(10a)-S₁₁ is, for example, an amplitude [mV] of a waveform ofthe difference detection signal S_(10a)-S₁₁, a duration [μsec] of thewaveform of the difference detection signal S_(10a)-S₁₁, the number ofzero cross counts [times] of the difference detection signalS_(10a)-S₁₁, energy [arb.] of the waveform of the difference detectionsignal S_(10a)-S₁₁, and a frequency [Hz] of the difference detectionsignal S_(10a)-S₁₁.

The extractor 27 inputs the respective pieces of feature amountinformation and time information of the difference detection signalsS_(10a)-S₁₁ to S_(10a)-S₁₁ to the second calculator 28.

The second calculator 28 receives the respective pieces of featureamount information and time information of the difference detectionsignals S_(10a)-S₁₁ to S_(10d)-S₁₁ from the extractor 27. The secondcalculator 28 divides the plurality of difference detection signalsS_(10a)-S₁₁ to S_(10a)-S₁₁ into groups based on whether the similaritiesof the feature amount information of the difference detection signalsS_(10a)-S₁₁ to S_(10a)-S₁₁ are a predetermined threshold (firstthreshold) or more. Then, the second calculator 28 recognizes thedifference detection signals S_(10a)-S₁₁ to S_(10a)-S₁₁ included in thesame group as the difference detection signals S_(10a)-S₁₁ toS_(10d)-S₁₁ of the same generation source.

Note that the similarity is determined according to a distance betweenthe feature amount information and the feature amount information. Thatis, the similarity is larger as the distance between different pieces ofthe feature amount information is closer. The second calculator 28calculates the distance between the pieces of feature amount informationby a predetermined distance function. The distance function is afunction for calculating, for example, a standard Euclidean distance, aMinkowski distance, or a Mahalanobis distance. Especially, theMahalanobis distance enables calculation of the distance, consideringcorrelation between the pieces of feature amount information, and canimprove classification accuracy of the groups.

The second calculator 28 calculates time difference information from thetime information of the difference detection signals S_(10a)-S₁₁ toS_(10d)-S₁₁ corresponding to the feature amount information with thesimilarity being a predetermined threshold or more (the feature amountinformation of the difference detection signals S_(10a)-S₁₁ toS_(10d)-S₁₁ included in the same group). The second calculator 28calculates positional information of the generation source of theelastic wave based on the positional information of the first sensors 10a to 10 d, the time difference information, and the propagating speed ofthe elastic wave. Here, the propagating speed of the elastic wave willbe described.

The propagation speed v of the elastic wave propagating in a material isexpressed by the following Equation (1), using elastic modulus K [Pa] ofthe material and density ρ₀ [kg/m³].

$\begin{matrix}{v = \sqrt{\frac{K}{\rho_{0}}}} & (1)\end{matrix}$

Further, the propagating speed v of the elastic wave propagating in astructure (three-dimensional body) is expressed by the followingEquation (2), in consideration of shearing modulus G of the material.

$\begin{matrix}{v = \sqrt{\frac{1}{\rho_{0}} \cdot \left( {K + {\frac{4}{3}G}} \right)}} & (2)\end{matrix}$

That is, the propagating speed of the elastic wave is determinedaccording to physical properties unique to the material. Therefore, thepropagation speed information calculated in advance for each material(the quality of the material of the structure) is stored by the secondcalculator 28 as a look-up table, for example, so that an appropriatepropagating speed according to the quality of the material of thestructure can be selected from the look-up table.

FIG. 10 is a diagram illustrating an example of propagating speedinformation of an embodiment. FIG. 10 illustrates an example of a caseof storing the propagating speed information as a look-up table. Forexample, the propagating speed v of when the quality of the material ofthe structure is iron is 5950 [m/s].

Next, a method of calculating the position of the generation source ofthe elastic wave by the second calculator 28 will be described. Forsimplification, a case of one dimension will be described in detail.Note that cases of two dimensions and three dimensions have the sameprinciple.

FIG. 11 is a diagram for describing an example of a position calculationmethod of an embodiment (in a case of one dimension). A case in which acrack of the structure is cased between the first sensor 10 a and thefirst sensor 10 b, and the elastic wave due to the crack is detected bythe first sensor 10 a and the first sensor 10 b will be described.

A distance between the first sensor 10 a and the first sensor 10 b is 1.Further, a distance from an intermediate point of the first sensor 10 aand the first sensor 10 b to the crack is Δx. At this time, when thefirst sensor 10 b detects the elastic wave after T seconds, and thefirst sensor 10 a detects the elastic wave after T+Δt seconds, the timedifference information Δt can be expressed by the following Equation(3).

$\begin{matrix}{{\Delta\; t} = {{\left( {\left( {\frac{1}{2} + {\Delta\; x}} \right) - \left( {\frac{1}{2} - {\Delta\; x}} \right)} \right)/v} = {2\Delta\;{x/v}}}} & (3)\end{matrix}$

Therefore, if the distance l between the first sensor 10 a and the firstsensor 10 b and the propagating speed v of the elastic wave are known,the second calculator 28 can calculate the distance Δx from theintermediate point of the first sensor 10 a and the first sensor 10 b tothe crack from Equation (3) by calculating the time differenceinformation Δt. That is, the second calculator 28 can calculate thepositional information of the crack (generation source of the elasticwave) from the time difference information Δt.

Next, a case of two dimensions will be briefly described.

FIGS. 12 and 13 are diagrams for describing an example of a positioncalculation method of an embodiment (a case of two dimensions). FIG. 12illustrates a case in which a crack is caused in the structure, and theelastic wave due to the crack reaches the first sensors 10 a to 10 d atthe propagating speed v [m/s]. Times when the elastic wave reaches therespective first sensors 10 a to 10 d are different among the firstsensors 10 a to 10 d. If time differences among receiving times of theelastic wave can be known, the generation source of the elastic wave canbe estimated to be positioned on a circumference ARC_a (radius Ta), acircumference ARC_b (radius Tb), a circumference ARC_c (radius Tc), anda circumference ARC_d (radius Td) having the respective first sensors 10a to 10 d as the centers, as illustrated in FIG. 13. That is, the secondcalculator 28 can calculate an intersection point of the circumferencesARC_a to ARC_d as the positional information of the generation source ofthe elastic wave.

Typically, by use of (the number of dimensions+1) first sensors 10, theposition of the generation source of the elastic wave can be calculated.Therefore, in a case of three dimensions, by use of four first sensors10, the position of the generation source of the elastic wave can becalculated. Further, calculation accuracy of the positional informationcan be further improved as the number of the first sensors 10 is larger.

Referring back to FIG. 1, when the calculated positional informationfalls outside a predetermined measurement range (does not satisfy apredetermined threshold), the second calculator 28 performs noiseprocessing of removing the feature amount information of the differencedetection signals S_(10a)-S₁₁ to S_(10d)-S₁₁ used for the calculation asnoises. The second calculator 28 inputs the feature amount informationand the positional information to the communication unit 29.

When having received the feature amount information and the positionalinformation from the second calculator 28, the communication unit 29transmits the feature amount information and the positional informationto the server device 50.

When having received the feature amount information and the positionalinformation from the signal processing device 20, the server device 50performs processing based on the feature amount information and thepositional information.

FIG. 14 is a diagram illustrating an example of a functionalconfiguration of the server device 50 of an embodiment. The serverdevice 50 of an embodiment includes a storage 51, a communication unit52, a display controller 53, and a diagnosis unit 54.

The storage 51 stores information. The information stored in the storage51 is the feature amount information and the positional informationacquired in the signal processing device 20, for example.

When having received the feature amount information and the positionalinformation from the signal processing device 20, the communication unit52 stores the feature amount information and the positional informationin the storage 51. The display controller 53 performs display controlbased on the feature amount information and the positional informationstored in the storage 51. The diagnosis unit 54 diagnoses the degree ofdeterioration of the structure based on the feature amount informationand the positional information stored in the storage 51. When there is aplace where total energy of the elastic wave becomes predeterminedenergy or more, the diagnosis unit 54 performs display of a warning thatindicates a risk of deterioration in the place, to the displaycontroller 53.

FIG. 15 is a diagram illustrating an example of display information thatindicates the positional information of an embodiment. FIG. 15illustrates an example of a case of displaying the generation source ofthe elastic wave with positional information 111 and the like.

FIG. 16 is a diagram illustrating an example of the display informationthat indicates cumulative energy of an embodiment. FIG. 16 illustrates acase of displaying the cumulative energy by a curved line 112. Thedisplay controller 53 performs control of displaying the displayinformation illustrated in FIG. 16, for example, when there is an inputthat indicates selection of the positional information 111 when thedisplay information illustrated in FIG. 15 is being displayed. Further,when a user specifies a selection range on a screen where the displayinformation illustrated in FIG. 15 is displayed, the cumulative energyof the elastic wave included in the selection range is displayed by thecurved line 112, whereby a feature can be more easily grasped. Theselection range is, for example, an inside of a square with a diagonalline from a dragged position to a dropped position specified by adrag-and-drop operation of a mouse, or an inside of a circle inscribedin the square, whereby operability can be further improved.

In FIG. 16, E₁ is a threshold used when the state of the deteriorationof the structure is diagnosed by the diagnosis unit 54. That is, thediagnosis unit 54 requests the display controller 53 to display awarning or the like that indicates that the degree of deterioration islarge at a time t₁ when a value of the cumulative energy becomes E₁.Accordingly, an administrator of the structure or the like can grasp ahigh possibility of causing a rupture of the structure before therupture of the structure is caused due to further development of thedeterioration. Note that the example of FIG. 16 indicates a case inwhich the rupture of the structure is caused at a time t₂. At and afterthe cumulative energy E₂, the cumulative energy E is sharply increaseddue to impact at the time of the rupture of the structure. Then, whenthe state of the structure becomes stable after the rupture, the elasticwave is not generated, and the cumulative energy E becomes constant.

Next, a detection method of an embodiment will be described.

FIG. 17 is a flowchart illustrating an example of a detection method(signal selection processing) of an embodiment. First, the firstamplifier 21 receives the detection signal S₁₀ from the first sensor 10,and the second amplifier 22 receives the reference signal S₁₁ from thesecond sensor 11 (step S1). Next, the first amplifier 21 amplifies thedetection signal S₁₀, and the second amplifier 22 amplifies thereference signal S₁₁ (step S2). Next, the first calculator 23 calculatesthe difference detection signal S₁₀-S₁₁ by subtracting the referencesignal S₁₁ from the detection signal S₁₀ (step S3).

Next, the generator 25 determines whether any one of the detectionsignals S_(10a) to S_(10d) is a threshold or more (step S4).

When any one of the detection signals is the threshold or more (Yes instep S4), the switch 24 a (the switch 24 b, the switch 24 c, or theswitch 24 d) inputs the difference detection signal S_(10a)-S₁₁(S_(10b)-S₁₁, S_(10c)-S₁₁, or S_(10d)-S₁₁) to the adjuster 26 and theextractor 27 until the predetermined time T passes (step S5).

When all the detection signals Snare less than the threshold (No in stepS4), the switch 24 a (the switch 24 b, the switch 24 c, or the switch 24d) inputs the detection signal S₁₀a (S_(10b), S_(10c), or S_(10d)) tothe generator 25 and the adjuster 26 (step S6).

FIG. 18 is a flowchart illustrating an example of a detection method(positional information calculation processing) of an embodiment. First,the extractor 27 receives the difference detection signals S_(10a)-S₁₁to S_(10d)-S₁₁ from the switch unit 24 (step S11). Next, the extractor27 stores the time information that indicates the times when theextractor 27 has received the respective difference detection signalsS_(10a)-S₁₁ to S_(10d)-S₁₁ (step S12). Next, the extractor 27 extractsthe feature amount information from the respective difference detectionsignals S_(10a)-S₁₁ to S_(10d)-S₁₁ (step S13).

Next, the second calculator 28 calculates the positional informationthat indicates the position of the generation source of the elastic wavefrom the time information stored in step S12 and the feature amountinformation extracted in step S13 (step S14). To be specific, the secondcalculator 28 divides the plurality of difference detection signalsS_(10a)-S₁₁ to S_(10d)-S₁₁ into groups based on whether the similaritiesof the feature amount information of the difference detection signalsS_(10a)-S₁₁ to S_(10d)-S₁₁ a predetermined threshold or more. Next, thesecond calculator 28 recognizes the difference detection signalsS_(10a)-S₁₁ to S_(10d)-S₁₁ included in the same group as the differencedetection signals S_(10a)-S₁₁ to S_(10d)-S₁₁ of the same generationsource. Next, the second calculator 28 calculates the time differenceinformation from the time information of the difference detectionsignals S_(10a)-S₁₁ to S_(10d)-S₁₁ corresponding to the feature amountinformation with the similarity being the predetermined threshold ormore (the feature amount information of the detection informationincluded in the same group). Next, the second calculator 28 calculatesthe positional information that indicates the positional information ofthe generation source of the elastic wave from the time differenceinformation, and the propagating speed v of the elastic wave accordingto the quality of the material of the structure.

Next, the communication unit 29 transmits the feature amount informationextracted in step S12 and the positional information calculated in stepS13 to the server device 50 (step S15).

FIG. 19 is a flowchart illustrating an example of a detection method(display processing) of an embodiment. First, the communication unit 52receives the feature amount information and the positional informationfrom the signal processing device 20 (step S21).

Next, the diagnosis unit 54 diagnoses deterioration of the structurebased on the feature amount information and the positional information(step S22). To be specific, the diagnosis unit 54 diagnoses thedeterioration of the structure by determining whether there is ageneration source where the cumulative energy of the elastic wavebecomes a predetermined threshold or more.

Next, the display controller 53 updates the display information to bedisplayed in the display device based on the feature amount informationand the positional information, and a diagnosis result obtained by theprocessing of step S22 (step S23). The display information is, forexample, the information of FIGS. 15 and 16, and the like.

Next, when the cumulative energy is the threshold or more (Yes in stepS24), the display controller 53 displays a warning indicating that thedegree of deterioration of the structure is large in the display device(step S25). When the cumulative energy is less than the threshold (No instep S24), the processing is terminated.

Finally, an example of a hardware configuration of the server device 50of an embodiment will be described.

FIG. 20 is a diagram illustrating an example of a hardware configurationof the server device 50 of an embodiment. The server device 50 of anembodiment includes a control device 201, a main storage device 202, anauxiliary storage device 203, a display device 204, an input device 205,and a communication device 206. The control device 201, the main storagedevice 202, the auxiliary storage device 203, the display device 204,the input device 205, and the communication device 206 are connectedthrough a bus 210. The server device 50 is, for example, a personalcomputer, a smart device, and the like.

The control device 201 executes a program read by the main storagedevice 202 from the auxiliary storage device 203. The main storagedevice 202 is memories such as a read only memory (ROM) and a randomaccess memory (RAM). The auxiliary storage device 203 is a hard diskdrive (HDD), a memory card, and the like. The storage 51 of FIG. 14corresponds to the main storage device 202 and the auxiliary storagedevice 203.

The display device 204 displays a state of the server device 50, and thelike. The display device 204 is a liquid crystal display, for example.The input device 205 is an interface for operating the server device 50.The input device 205 is, for example, a keyboard, a mouse, and the like.When the server device 50 is the smart device such as a smart phone anda tablet terminal, the display device 204 and the input device 205 are atouch panel, for example. The communication device 206 is an interfacefor being connected to a network.

The program executed in the server device 50 of an embodiment isrecorded in storage media readable by a computer, such as a CD-ROM, amemory card, a CD-R, and a digital versatile disk (DVD) in aninstallable format file or an executable format file, and is provided asa computer program product.

Further, the program executed in the server device 50 of an embodimentmay be stored on a computer connected to a network such as the Internet,and provided by being downloaded through the network. Further, theprogram executed in the server device 50 of an embodiment may beprovided through the network such as the Internet without beingdownloaded.

Further, the program of the server device 50 of an embodiment may beprovided by being incorporated in a ROM or the like in advance.

The program executed in the server device 50 of an embodiment is amodule configuration including the function blocks (the communicationunit 52, the display controller 53, and the diagnosis unit 54) of FIG.14. As actual hardware of the function blocks, the program is read fromthe storage medium and executed by the control device 201, so that thefunction blocks are loaded onto the main storage device 202. That is,the function blocks are generated on the main storage device 202. Notethat a part or all of the function blocks of FIG. 14 may be realized byhardware such as an integrated circuit (IC) instead of being realized bysoftware.

As described above, in the detection system 1 of an embodiment, theplurality of first sensors 10 detects the elastic wave generated fromthe structure, and converts the elastic wave into the detection signalS₁₀. Further, the second sensor 11 detects the noises propagating fromsurroundings, and converts the noises into the reference signal S₁₁.Further, the first calculator 23 calculates the plurality of differencedetection signals S₁₀-S₁₁ based on the respective detection signals S₁₀and the reference signal S₁₁. The second calculator 28 then calculatesthe position of the generation source of the elastic wave from theplurality of difference detection signals S₁₀-S₁₁. Accordingly,according to the detection system 1 of an embodiment, the elastic wavecan be highly accurately detected without depending on a detectionenvironment of the elastic wave.

Note that, in the description of the detection system 1, configurationsof the function blocks included in the respective devices may bechanged. For example, the second calculator 28 of the signal processingdevice 20 may be realized in the server device 50. The second calculator28 is realized in the server device 50, so that when the calculatedpositional information is outside the predetermined measurement range(when the calculated positional information does not satisfy thepredetermined threshold), a condition of the threshold used fordetermination of the noise processing of removing the feature amountinformation of the difference detection signals S_(10a)-S₁₁ toS_(10d)-S₁₁ used for the calculation as noises can be flexibly changed.That is, deviation of the installation position of the first sensor 10,a condition of the structure to be measured, a weather condition, andthe like can be flexibly changed. Therefore, the second calculator 28can more effectively remove the noises.

Further, in this case, non-calculation of the positional information inthe signal processing device 20 can reduce the power consumption of thesignal processing device 20. Accordingly, the signal processing device20 can be operated by a solar battery, a vibration power generationmodule, and the like, whereby the signal processing device 20 can beinstalled in a place with no power supply.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A detection system comprising: a plurality offirst sensors each configured to detect an elastic wave generated from astructure, and convert the elastic wave into a detection signal; asecond sensor configured to detect a noise propagating fromsurroundings, and convert the noise into a reference signal; a firstcalculator configured to calculate a plurality of difference detectionsignals based on the respective detection signals, each differencedetection signal being calculated by subtracting the reference signalfrom the detection signal; and a second calculator configured tocalculate a position of a generation source of the elastic wave from theplurality of difference detection signals, wherein a distance b betweenthe second sensor and the first sensor closest to the second sensor islarger than a distance a between the closest first sensor and the firstsensor farthest from the closest first sensor, and the first calculatorcancels, without subtracting the reference signal from the detectionsignal, the reference signal that is obtained after a time obtained bydividing the distance a by a speed of the elastic wave, the timestarting when the elastic wave first reached any one of the plurality offirst sensors.
 2. The system according to claim 1, wherein the firstcalculator performs calculation to calculate the plurality of differencedetection signals within a range of a time obtained by dividing amaximum distance between the first sensors by the speed of the elasticwave when the elastic wave has first reached any one of the firstsensors.
 3. The system according to claim 1, wherein the second sensoris installed in the structure through a silencing material thatattenuates or reflects the elastic wave reaching the second sensor. 4.The system according to claim 1, further comprising: a first amplifierconfigured to amplify the detection signal input from the first sensor,and input the amplified detection signal to the first calculator; and asecond amplifier configured to amplify the reference signal input fromthe second sensor, and input the amplified reference signal to the firstcalculator.
 5. The system according to claim 4, further comprising anadjuster configured to receive the detection signal or the differencedetection signal, and adjust the degrees of amplification of the firstamplifier and the second amplifier based on the detection signal or thedifference detection signal.
 6. The system according to claim 1, furthercomprising an extractor configured to extract feature amount informationindicating a feature of each difference detection signal from the eachdifference detection signal, wherein the second calculator calculates asimilarity of the feature amount information, and calculates theposition of the generation source of the elastic wave based on timedifference information indicating a time difference between times whenthe difference detection signals from which the feature amountinformation having the similarity being a first threshold or more hasbeen extracted have been received, positional information indicatingpositions of the plurality of first sensors, and a propagating speed ofthe elastic wave.
 7. The system according to claim 6, wherein thefeature amount information includes at least one of an amplitude of awaveform of the difference detection signal, a duration of the waveformof the difference detection signal, the number of zero cross counts ofthe difference detection signal, energy of the waveform of thedifference detection signal, and a frequency of the difference detectionsignal.
 8. The system according to claim 7, further comprising: a switchunit configured to select either the detection signal or the differencedetection signal according to a selection signal; and a generatorconfigured to generate the selection signal indicating that thedifference detection signal is being selected until a predetermined timepasses when the detection signal received from the switch unit is asecond threshold or more, wherein the extractor receives the differencedetection signal from the switch unit.
 9. A detection method comprising:detecting, by each of a plurality of first sensors, an elastic wavegenerated from a structure to convert the elastic wave into a detectionsignal; detecting, by a second sensor, a noise propagating fromsurroundings to convert the noise into a reference signal; calculating,by a first calculator, a plurality of difference detection signals, eachdifference detection signal being calculated by subtracting thereference signal from the detection signal; and calculating, by a secondcalculator, a position of a generation source of the elastic wave fromthe plurality of difference detection signals, wherein a distance bbetween the second sensor and the first sensor closest to the secondsensor is larger than a distance a between the closest first sensor andthe first sensor farthest from the closest first sensor, and thecalculating by the first calculator cancels, without subtracting thereference signal from the detection signal, the reference signal that isobtained after a time obtained by dividing the distance a by a speed ofthe elastic wave, the time starting when the elastic wave first reachedany one of the plurality of first sensors.